In the circuit and system theory as well as in the practice it is of interest to minimize the output impedance of power converters of a voltage-source type in both steady state and transient. See, for example, K. K. Sum, "Switch Mode Power Conversion", Marcel Dekker, Inc., 1984, pp.196-200, P. R. K. Chetty, "Switch-Mode Power Supply Design". TAB Books, Inc., 1986, pp.84-87, K. Billings, "Switchmode Power Supply Handbook", McGraw-Hill, 1989, pp.3.228, and PCIM magazine, October 1989, pp.29.
Furthermore, in order to achieve mathematically complete, and thus ideal, load-independent operation, it can be shown that in a system of interest an impedance of interest should be forced to zero whereby this statement applies to both power converters and electric motor drives employing any kind of motor including dc, synchronous and asynchronous ac, and step motors.
All known techniques produce less or more successful minimization of the impedance of interest, usually in proportion to their complexity, in an attempt to optimize the solution to this problem. One such optimization is given in the article by R. Redl and N. O. Sokal, "Near-Optimum Dynamic Regulation of DC-DC Converters Using Feed-Forward of Output Current and Input Voltage With Current-Mode Control", IEEE Transactions on Power Electronics, VOL.PE-1, No.3, July 1986, pp.181-192, but is not, as such, applicable to, for example, drives.
None of the presently known techniques produces a zero impedance.
A particular and specific applications of a zero-impedance converter are described in the U.S. Pat. No. 4,885,674, December 1989, entitled "Synthesis of Load-Independent Switch-Mode Power Converters" by these same two inventors L. J. D. J. Varga and N. A. Losic as well as in the two copending and coassigned applications of N. A. Losic and L. J. D. J. Varga, entitled "Synthesis of Load-Independent DC Drive System", patent application Ser. No. 07/323,630, November 1988, and "Synthesis of Load-Independent AC Drive systems", patent application Ser. No. 07/316,664, February 1989.